Continuous world population growth and sustained development of the global economy has given rise to a rapid increase in the demand for lighting. Lighting is one of the most energy-consuming demands, as most people in developed or developing countries work and live in rooms with artificial lighting. However, the peak demand for indoor lighting takes place in the daytime when there is abundant sunlight. 40% of power for lighting is consumed during this time period. Therefore, development and utilization of inexhaustible solar energy resources can be of great value to energy-savings. Such savings can, in turn, greatly reduce the CO2 discharge from power plants, resulting in a better ecological environment and paving a strategic route to sustainable economic development.
Furthermore, as land resources become more expensive in modern society, residential houses are generally designed in an architectural layout that maximizes exterior wall exposure to sunlight in an effort to meet the lighting requirements of residents. In many large public buildings, for instance shopping malls, large, open architectural areas (referred to as skylights) are designed, which render precious space useless. Even so, such large buildings remain mainly dependant on artificial lighting. To minimize waste of space resources and obtain good natural lighting, people have been exploring various light collecting technologies with the potential to maximize the natural light environment
For more than two decades, the technology to harness sunlight for interior lighting has been a focus of research in many countries. This technology can be roughly grouped into three types: light transmission with light pipes, light transmission with optical fibers and direct reflection lighting with planar reflectors, such as the prismatic light pipes produced by the 3M Company of Minneapolis, Minn., and the optical fibers light collector Himawari system made in Japan. Although such media as light pipes and optical fibers have some superiority in light transmission, they are expensive and it is difficult to apply them in practical ways.
Direct reflection lighting with planar reflectors is an economic and practical way to harness light with a reasonable performance to price ratio. The planar reflectors are installed on the tops of buildings, allowing the interiors direct access to reflected sunlight; secondary reflectors can be installed to further reflect light into rooms. For instance, in U.S. Pat. Nos. 4,883,340, 4,586,488 and 4,922,088, light is obtained by reflecting sunlight using planar reflectors. In U.S. Pat. No. 4,883,340, a number of parallel planar reflectors are fixed on supports. At the lower end of the supports, an azimuth angle adjustment mechanism controls the azimuth angle of the planar reflectors. However, as the altitudinal angle of the sun changes continuously throughout the day, the direction of the sunlight reflected by planar reflectors also changes. As a result, the projection of light from this light collection device moves continuously with the change of the sun's altitudinal angle, making it impossible to get light in a fixed direction. Furthermore, in this patent, the spacing of planar reflectors is fixed, thus, there may be unlighted spaces between the projections of reflected light from the planar reflectors at higher sun altitudinal angles, and overlapping may occur at lower altitudinal angles To avoid such overlapping, the planar reflectors need to be more widely spaced, which results in an oversized installation and wasted space. Both devices in U.S. Pat. Nos. 4,586,488 and U.S. Pat. No. 4,922,088 have realized reflection in a fixed direction, but due to structural defect, two planar reflectors can only be arranged on separate sides of the turning shaft, leaving an unlighted space in the reflected light projection.